The objective of this research is to determine the molecular structure of ubiquitin, using protein x-ray crystallographic techniques. This small protein has been sequenced and has a molecular weight of 8565 daltons. Although its exact role in the cell is unknown, it has been implicated in transcription and intracellular ATP-dependent protein degradation. These two functions involve the formation of ubiquitin-protein conjugates. The polypeptide chain has been traced, and the structure has been determined at 2.8 Angstrom resolution. Refinement of the structure at the highest possible resolution (approximately 1.0 Angstrom) is the ultimate goal. Crystals of yeast ubiquitin have been grown, and comparison of the structures of mammalian ubiquitin and yeast ubiquitin will also be undertaken as the refinement progresses.